Windows NT/2K/XP/2003 boot files (NTLDR/NTDETECT.COM/BOOT.INI) or Vista/2008 (BOOTMGR/BCD) need normally to be on a Primary partition (unless a boot manager is used) but OS can be installed to a Logical Volume inside Extended allright.

Besides, it is also possible to make a Logical Volume inside Extended "behave" as a Primary partition, by fixing the bootsector.